1- Nikon- If you try this lens you will know why the price is what it is. I just bought this lens a week or so ago while it was still on sale for $2099. It is AMAZING glass. Great contrast, great colors and very very fast AF. VR is amazing (hand held down to 1/6 and no blur for me). Built like a tank. Hold it and use it and you will want one!

2-Tamron- Tried the new 70-200 2.8 VC in the store. Not as sharp as the nikon 2.8 but did get better at f4. VC is great. Build is not solid as nikon. AF not as fast to me.

3-SIGMA- Not as sharp as the tamron at 2.8 and not close to the nikon at 2.8. Would buy the tamron if you cant affoard the nikon.

At the end of the day, I would save up for the nikon if I was on a budget.